This invention relates to a process for converting weakly or non-coking or caking coals to metallurgical coke, pitch, electrode carbon and other useful products.
In the past several decades coking coals with low sulfur content suitable for making metallurgical coke have become increasingly difficult to find and more costly to produce in the United States and in other countries. These problems could be greatly alleviated if a practical process could be found for converting non-coking subbituminous coal and lignite to coke. Such processes would be especially applicable in geographical locations, such as the Western part of the United States, where immense reserves of low rank non-coking coals are available.
One object of this invention is to provide a process whereby weakly or non-coking or caking coals can be economically converted into coke suitable for blast furnace or other metallurgical use.
At the present time the aluminum and electrochemical industries cannot use coke or calcined carbon for electrodes which has been prepared from coal, as this is generally too high in ash to be satisfactory. Consequently they use coke obtained from petroleum such as from delayed coking or other refining processes. With the increased price of crude oil petroleum coke has also increased greatly in price, and it has become difficult to obtain coke low in impurities including sulfur.
Electrodes, such as used in the aluminum industry for example, are prepared by mixing crushed petroleum coke (of high purity and especially low in silica, iron and sulfur) with about 25 percent by weight of pitch. This mixture is pressed into the electrode shape and then calcined at high temperature to produce a dense, strong electrode with good electrical conductivity. The pitch which is the binder in the electrode has in the past been obtained from the tar produced in the operation of coke ovens. This material now commands a high price and is in short supply.
A second object of this invention is, therefore, to provide a process for converting all ranks of coal except anthracite to both pitch and electrode carbon of high purity for the aluminum, electro-chemical, and other industries.
Aromatic chemicals for the preparation of raw materials for plastics and fibers are also obtained from tar and oils from coke ovens. Growth in this section of the chemical industry has far outstripped the growth rate for coke ovens and consequently only about 10 percent of these products can now be supplied by the coking industry. The petroleum industry has been able to supply this increasing demand. However, since crude oil consists mainly of aliphatic compounds, complex hydroforming processes are necessary to produce aromatics. High prices and short supplies have resulted.
It is, therefore, a third object of this invention to provide a relatively simple and economic process which makes use of the natural ring structure of coal to provide aromatic chemicals for the plastic and related industries.
It is well known that sulfur is objectional in metallurgical coke. Sulfur limits are even lower for the coke and pitch used to make electrodes. Another object of this invention is to eliminate the sulfur from coal during the conversion process.
Other advantages of the process, including good control of product composition, simplicity and low capital cost and operating costs, will become apparent during the description thereof.